Persistence and Ecological Impact of Ionic Liquids in Soil

Purpose of Review

Ionic liquids (ILs) are organic salts composed of organic cations and organic/inorganic anions that are liquid at room temperature. ILs are considered “green” solvents; however, with the widespread application of ILs in the chemical industry, research has determined that ILs may persist in the soil environment and exert toxicological impact on ecological receptors. This paper reviews the status of ILs residues in soil, their effect on soil biota, limitations of current studies, and emerging research areas for ILs.

Recent Findings

The ILs change the physical and chemical properties of soil by reducing pH and improving electrical conductivity. Ionic liquids may be absorbed by plants and animals, causing oxidative stress and DNA damage. Exposure to ILs may also impact soil microorganisms, changing the structure of soil microbial community, and impacting their functionality.

Summary

This review highlights that IL fate and transport are influenced by the size of the alkyl chain. Those with longer carbon chains with the same anion, normally have smaller median lethal concentrations (LC₅₀) to earthworms, which indicates that IL toxicity increases with increasing carbon chain length. As such, the relationship between structure, mobility, and toxicity should be considered in the development and application of ILs. In the future, long-term monitoring of ILs residues and distribution in the environment will be required. Degradation products and the toxicity of degradation products should also be further identified.

Graphical Abstract

This paper summarized the ways in which ILs enter the soil environment, identified methods for the detection of ILs in environmental matrices, and detailed the environmental behavior (absorption, transfer/biological uptake, and degradation) of ILs in soil including ecological impacts on invetebrates, plants, and microorganisms.